Load cell to frame interface for hospital bed

ABSTRACT

A load cell apparatus has a load cell adapted to couple to a first structure. The load cell comprises a load cell body and a sensor. The sensor provides an output signal indicative of an amount of weight applied to the load cell. A stud extends away from the load cell body. The load cell apparatus has a stud receiver including a space in which a portion of the stud is received. A set of rollers are coupled to one of the stud receiver and a second structure and contact the other of the stud receiver and the second structure.

This application claims the benefit, under 35 U.S.C. § 119(e), of U.S.Provisional Patent Application Ser. No. 60/609,484 which was filed Sep.13, 2004 and which is hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to apparatuses, such ashospital beds, having integrated weighing systems. More particularly,the disclosure relates to interfaces between load cells of weigh scalesystems and the structures which support the load cells.

Various apparatuses, such as patient support apparatuses, having weighscale systems for weighing loads, such as patients, are known. Suchweigh scale systems sometimes include load cells that deflect under anapplied load. Some conventional load cells include a block (also knownas a load beam) and one or more strain gages mounted to the block.Deflection of the block due to an applied load changes the shape of thestrain gages resulting in a change in the resistance of the straingages. Generally, a known input voltage is applied to the strain gagesand an output signal from the strain gages varies as the resistance ofthe strain gages vary to provide a signal indicative of the load appliedto the load cell. Some conventional load cells include other types ofsensors, such as optical sensors or capacitive sensors, rather thanstrain gages, that measure the size of gaps between elements of a loadcell system. It is desirable, of course, for load cells to sense appliedloads with a high degree of accuracy and repeatability.

SUMMARY OF THE INVENTION

The present invention comprises one or more of the features recited inthe appended claims and/or the following features which, alone or in anycombination, may comprise patentable subject matter:

A combination may comprise a first structure, a second structure, and aload cell coupled to the first structure. The load cell may have a loadcell body and a sensor. The sensor may provide an output signalindicative of an amount of weight applied to the load cell. A stud mayextend away from the load cell body. A stud receiver may have a space inwhich a portion of the stud is received. A set of rollers may be coupledto one of the stud receiver and the second structure and the rollers maycontact the other of the stud receiver and the second structure.

The sensor may comprise a strain gage, a resistive element, a capacitor,a transducer using shaped magnetic field technology, an optical sensor,a transducer that emits electromagnetic energy, a transducer thatreceives electromagnetic energy, a linear variable displacementtransducer, or any other type of device that is operable to provide asignal indicative of an amount of weight applied to the load cell. Thespace may comprises a substantially cylindrical hole or a substantiallytriangular hole. The space may have a pair of inclined surfaces thatcontact the stud. The stud may have a cylindrical portion or a sphericalportion. The cylindrical portion may have a stud diameter that issmaller than a diameter of the substantially cylindrical hole. Thesubstantially triangular hole may have three apexes that are spaced-fromthe stud. The apexes of the triangular hole may be rounded. The loadcell body may have a threaded hole and the stud may have a threadedportion that threads into the threaded hole. The stud receiver mayrotate about the stud when the second structure tilts relative to thefirst structure. The stud receiver may be made of a plastic material andthe stud may be made of a metal material.

The set of rollers may comprise one roller or multiple rollers. The setof rollers may roll upon the second structure when the second structuretilts relative to the first structure. The set of rollers may roll uponthe stud receiver when the second structure tilts relative to the firststructure. The stud may extend substantially horizontally relative tothe load cell body along a first substantially horizontal axis and eachof the set of rollers may rotate about a respective second substantiallyhorizontal axis. The stud receiver may have at least oneroller-receiving pocket in which at least a portion of each roller ofthe set of rollers is received. The stud receiver may comprise ahorizontal wall underlying the at least one roller-receiving pocket. Oneor more vertical walls may be situated between the roller-receivingpockets. The roller-receiving pockets may each be open at a top surfaceand at a respective end surface of the stud receiver. Each roller of theset of rollers may extend upwardly beyond a top surface of the studreceiver.

The stud receiver may have a pair of vertical walls and at least part ofeach roller of the set of rollers may be situated between the pair ofvertical walls. A set of shafts may extend across a gap defined betweenthe pair of vertical walls and each roller of the set of rollers may bemounted for rotation on a respective shaft of the set of shafts. Thecombination may further comprise a set of bushings that are interposedbetween a respective roller of the set of rollers and the associatedshaft. The combination may further comprise a set of bearings, each ofwhich may have rolling elements and each of which may be interposedbetween a respective roller of the set of rollers and the associatedshaft. The first and second vertical walls may have first and secondholes, respectively, that receive ends of respective shafts. The firstholes may each have a diameter that is larger than a diameter of thesecond holes. Each shaft of the set of shafts may have a shoulder thatcontacts the second vertical wall. The stud receiver may have a set ofshaft retainers coupled to the first vertical wall. Each shaft retainermay be heat staked over an end of a respective shaft.

The combination may further comprise a bracket that couples the loadcell body to the first structure. The bracket may have a bottom portionthat underlies the load cell body and at least one side portion thatextends between the bottom portion and the first structure. The sideportion may be fastened to the first structure and the load cell bodymay be fastened to the bottom portion. The bracket may comprise a bottomportion and two side portions extending upwardly from the bottom portionsuch that the bracket is U-shaped in cross section. The load cell bodymay sit atop the bottom portion. At least part of the first structuremay be situated above the load cell body and between the two sideportions of the bracket.

The first structure may comprise a lift mechanism of a patient supportapparatus and the second structure may comprises a frame of the patientsupport apparatus. The patient support apparatus may comprise a hospitalbed. The patient support apparatus may have a length dimension definedbetween a head end and a foot end of the patient support apparatus andthe stud may have an axis that is substantially perpendicular to thelength dimension of the patient support apparatus. The lift mechanismmay be extendable and retractable to change an elevation of the upperframe. The load cell body may be coupled to the lift mechanism so as tomove upwardly and downwardly without tilting as the lift mechanismextends and retracts.

The lift mechanism may comprise a telescoping column and a frame membercoupled to an upper region of the telescoping column. An end of theframe member of the lift mechanism may extend from the telescopingcolumn toward a frame member of the upper frame. The load cell body maybe coupled to the end of the frame member of the lift mechanism. Theupper frame of the patient support apparatus may comprise a frame memberhaving a C-shaped cross section defining a channel in which the studreceiver is situated. Thus, the frame member may comprise a top wall, abottom wall, and a side wall extending between the top and bottom walls.The set of rollers may contact an undersurface of the top wall of theframe member. The lift mechanism may be operable to change the elevationof the upper frame and, as the upper frame changes elevation, the set ofrollers my roll on the undersurface of the top wall.

In accordance with this disclosure, a patient support apparatus may havea base frame, an upper frame above the base frame, and a pair of liftmechanisms operable to raise, lower, and tilt the upper frame relativeto the base frame. A first pair of load cell assemblies may couple oneof the lift mechanisms to the upper frame and a second pair of load cellassemblies may couple the other of the lift mechanisms to the upperframe. Each load cell assembly of the first pair of load cell assembliesmay comprise a load cell coupled to the first lift mechanism and arolling carrier. The rolling carrier may have a carrier body and a setof rollers coupled to the carrier body and contacting the upper frame.The rollers may roll upon the upper frame when the upper frame is tiltedrelative to the base frame. Alternatively, a set of rollers may becoupled to the upper frame and roll upon the rolling carrier when theupper frame is tilted relative to the base frame. Each load cellassembly of the second pair of load cell assemblies may comprise a loadcell coupled to the second lift mechanism and a fixed carrier coupled tothe frame. Each load cell may comprise a load cell body and a studextending from the load cell body. Each of the rolling carriers andfixed carriers may have a space that receives the respective stud. Therolling carriers and the fixed carriers may pivot relative to therespective studs when the upper frame is tilted relative to the baseframe.

Additional features, which alone or in combination with any otherfeature(s), including those listed above and those listed in the claims,may comprise patentable subject matter and will become apparent to thoseskilled in the art upon consideration of the following detaileddescription of illustrative embodiments exemplifying the best mode ofcarrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is a perspective view, with portions broken away, showing ahospital bed having a base frame, a pair of lift mechanisms at ends ofthe base frame, an upper frame carrying an articulated patient-supportdeck, and a plurality of load cell assemblies connecting the upper frameto the lift mechanisms;

FIG. 2 is an enlarged perspective view of one of the load cellassemblies, a portion of the one of the lift assemblies, and a portionof the upper frame at a head end of the patient support apparatusshowing a movable stud receiver of one of the load cell assembliessituated in a C-shaped frame member of the upper frame, the movable studreceiver having a hole aligned with a stud that extends from a load cellbody (mostly in phantom) of the associated load cell assembly;

FIG. 3 is an enlarged perspective view of one of the load cellassemblies, a portion of the other of the lift assemblies, and a portionof the upper frame at a foot end of the patient support apparatusshowing a fixed stud receiver situated in another C-shaped frame memberof the upper frame, the fixed stud receiver having a hole aligned with astud that extends from a load cell body (mostly in phantom) of theassociated load cell assembly;

FIG. 4 is an exploded perspective view showing a portion of one of thelift assemblies, a portion of the upper frame, and the components of oneof the load cells assemblies that interconnect the associated liftassembly with the upper frame;

FIG. 5 is a cross sectional view, taken along line 5—5 of FIG. 2,showing a pair of rollers coupled to one of the stud receivers, the studreceiver having a vertical wall between the rollers and a horizontalwall underlying the rollers, the hole which receives the stud beingsituated generally in the area where the vertical and horizontal wallsmeet, and the rollers contacting an upper wall of a frame member of theupper frame;

FIG. 6 is a cross sectional view, taken along line 6—6 of FIG. 5,showing the load cell body coupled to a bottom wall of a bracket thatextends downwardly from a frame member of the associated lift mechanism,the frame member of the upper frame being C-shaped to define a channelin which the stud receiver is situated, and the stud extending from theload cell body into the hole of the stud receiver;

FIG. 7 is a side elevation view of part of the patient-supportapparatus, with portions broken away, showing the upper frame moved to ahorizontal position by the lift assemblies and the movable stud receiveron the right side of the page being in a first position a first distanceaway from a head end of the upper frame;

FIG. 8 is a side elevation view, similar to FIG. 7, showing the upperframe moved to a reverse Trendelenburg position by the lift assembliesand the movable stud receiver being in a second position closer to thehead end of the upper frame;

FIG. 9 is a side elevation view, similar to FIG. 8, showing the upperframe moved to a Trendelenburg position by the lift assemblies and themovable stud receiver being in the second position closer to the headend of the upper frame;

FIG. 10 is an exploded perspective view showing a portion of anotherembodiment of a stud receiver having a triangular hole and showing aportion of an associated cell body having a stud with a cylindricalportion aligned for insertion into the triangular hole; and

FIG. 11 is a cross sectional view through a portion of the stud receivershowing the cylindrical portion of the stud received in the triangularhole.

DETAILED DESCRIPTION OF THE DRAWINGS

Load cell apparatuses are described herein as being used in a weighingsystem of a patient support apparatus, such as a hospital bed. However,the load cell apparatuses described herein are not limited to use inpatient support apparatuses and those skilled in the art will appreciatethat the load cell apparatuses disclosed herein may be used in a widevariety of applications where loads are sensed.

According to this disclosure, a patient support apparatus 20 has a baseframe 22 to which a plurality of casters 24 are coupled, an upper frame26 above base frame 22, a first lift mechanism 28 near a head end 30 ofapparatus 20, and a second lift mechanism 32 near a foot end 34 ofapparatus 20 as shown in FIG. 1. Illustrative apparatus 20 is a hospitalbed and therefore, apparatus is sometimes referred to herein as “bed20.” However, the teachings of this disclosure are applicable to allsort of devices that carry loads including other types of patientsupport apparatuses, such as stretchers, operating room tables, chairs,infant incubators, radiant warmers, imaging tables, and the like.

Illustrative bed 20 further comprises an articulated patient supportdeck 36 which carries a support surface 38, such as a mattress, as shownin FIG. 1. Bed 20 also has a first pair of siderails 40 coupled to ahead section of deck 36, a second pair of siderails 42 coupled to frame26, and a footboard 44 coupled to frame 26 near foot end 34 of bed 20.Siderails 40, 42 are movable between respective raised positions, shownin FIG. 1, in which at least portions of siderails 40, 42 extend abovesupport surface 38, and lowered positions (not shown), in whichsiderails are below support surface 38 to facilitate patient egressfrom, and ingress onto, support surface 38.

Bed 20 includes a weighing system that is operable to weigh a patientsupported on surface 38. The weighing system comprises a first pair ofload cell assemblies 46 that couple to first lift mechanism 28 and toupper frame 26 adjacent head end 30 of bed 20 as shown in FIG. 1. Theweighing system further comprises a second pair of load cell assemblies48 that couple to second lift mechanism 32 and to upper frame 26adjacent foot end 34 of bed 20. Assemblies 46, 48 each comprise a loadcell 50 which, in turn, each comprise a load cell body 52 and one ormore sensors 54 as shown in FIG. 4. In some embodiments, the sensors 54of load cells 50 comprise one or more strain gages coupled to bodies 52.In such embodiments, the strain gages may include resistive elementsarranged in a Wheatstone bridge configuration. In other embodiments, thesensors of load cells 50 comprise one or more of the following: acapacitor, a transducer using shaped magnetic field technology, anoptical sensor, a transducer that emits electromagnetic energy, atransducer that receives electromagnetic energy, and a linear variabledisplacement transducer. Thus, this disclosure contemplates that sensors54 of load cells 50 may be any type of device that is operable toprovide a signal indicative of an amount of weight applied to load cells50.

Due to the weight carried by load cells 50, including the weight of anypatient supported on surface 38, load cell bodies 52 deflect. Thedeflection of bodies 52 is sensed by sensors 54 which provide outputsignals indicative of the amount of weight or load applied to therespective load cells 50. For example, in embodiments in which sensors50 are strain gages, a known input voltage is applied to the straingages and, as bodies 52 deflect due to the application of the load, theresistances of the strain gages change thereby resulting in a change inthe output signal from the strain gages. The output signals from sensors54 are coupled electrically to circuitry which conditions and/orprocesses the output signals to determine the weight of the patient onbed 20. For example, the output signals from sensors 54 comprise analogvoltage or current signals that are fed to one or more analog-to-digitalconverters, in some instances after amplification, and a digital signalfrom the analog-to-digital converter is fed to a microcontroller and/ormicroprocessor which processes the digital signals in accordance with anassociated software program to determine the weight of the patient. Ofcourse, if a microcontroller having an integrated analog-to-digitalconverter is used, then analog signals from sensors 54, or analogsignals from amplifiers coupled to sensors 54, are fed directly to themicrocontroller. All types of circuitry for conditioning and/orprocessing output signals from sensors 54 to determine the weight of apatient are intended to fall within the scope of this disclosure.

Bed 20 has various user inputs accessible to caregivers and to patientsfor controlling various functions of bed 20, including controlling theweighing system of bed 20, as is well know in the art. Such user inputsare provided on siderails 40 and, in some embodiments, on footboard 44.Bed 20 also has a display which displays information, such as the weightof the patient supported on bed 20. The display is provided on one ofsiderails 40, 42 in some embodiments, and on footboard 44 in otherembodiments. The various user inputs and the display are notillustrated, but these are well known in the art. In some embodiments,the user inputs for controlling functions of bed 20 and/or the displayare provided on a hand-held controller that communicates with the maincontrol circuitry of bed 20 either via a wired or wireless connection.

Some of the user inputs of bed 20 are used to raise or lower liftmechanisms 28, 32 to selectively raise, lower, or tilt upper frame 26relative to base frame 22. In the illustrative example, lift mechanisms28, 32 each comprise a telescoping column 56 having a lower segment 58coupled to base frame 22 and an upper segment 60 that extends andretracts relative to lower segment 58 as indicated by double-headedarrow 61 shown in FIG. 1. In other embodiments, telescoping columns 56have more than two segments. A driver such as a linear actuator,hydraulic actuator, a motorized jack screw, or the like is providedwithin each of columns 56 and is operable, either directly or via alinkage mechanism such as a scissors linkage, to extend and retractsegment 60 relative to segment 58. In addition, lift mechanisms otherthan telescoping columns are within the scope of this disclosure. Forexample, any of a number of arrangements of links or arms may extendbetween frames 22, 26 and may be driven by a driver to selectivelyraise, lower, or tilt frame 22 relative to frame 26. In addition, one ormore drivers, such as a motorized jack screw, may couple directly toframes 22, 26 and may be operated to selectively accomplish similarmovement of upper frame 26 relative to base frame 22.

Lift mechanisms 28, 32 each have a frame member 62 that extendslaterally relative to bed 20. That is, frame members 62 are generallyperpendicular to a long dimension of bed 20 defined between head end 30and foot end 34. Frame members 62 are each coupled to an upper region ofthe associated segment 60 of telescoping columns 56 as shown best inFIG. 4. In the illustrative example, sidewalls 64 of upper segments 60each have a notch 66, one of which is shown in FIG. 4, through which theassociated frame member 62 extends. Thus, end portions 68 of framemembers 62 extend laterally outwardly beyond respective sides oftelescoping columns 56. A pair of brackets 70 are mounted to segment 60in the interior region thereof and one or more fasteners, such as bolts72, one of which is shown in FIG. 4, couple frame members 62 to brackets70. Fasteners 72 also couple a cover 73 to the upper end of telescopingcolumns 56 in the illustrative example.

Load cell assemblies 46, 48 each include a bracket 74 that couples torespective end portions 68 of the associated frame members 62 as shownin FIGS. 2–4. Brackets 74 each have a horizontal bottom portion 76 and apair of vertical side portions 78 extending upwardly from bottom portion76. Thus, brackets 74 are U-shaped in cross section. In the illustrativeembodiment, portions 76, 78 comprise generally flat plates. Load cellbody 52 of each load cell 50 is coupled to bottom portion 76 of therespective bracket 74 by a pair of bolts or screws 80 that extendthrough respective apertures 82 in portions 76 and that thread intothreaded holes 84 formed in load cell bodies 52 as shown in FIGS. 4 and6.

Load cell bodies 52 are sometimes referred to in the art as load cellblocks or load beams. Illustrative load cell bodies 52 each have a firstenlarged end portion 86, a second enlarged end portion 88, and anecked-down portion 90 interconnecting portions 86, 88. However, loadcell bodies of all shapes and configurations are intended to fall withinthe scope of this disclosure. In the illustrative embodiment, threadedholes 84 are formed in end portion 86 of each load cell body 52 andscrews 80 fasten end portions 86 tightly against upper surfaces 92 ofportions 76 of respective brackets 74 as shown in FIG. 6. Optionally,washers or other spacers may be provided between portions 86 of bodies52 and portions 76 of brackets 74, if desired. End portions 88 of bodies52 are configured so that, under normal conditions in which bed 20 issupporting less than a “maximum” load, a slight gap exists between abottom surface 94 of each of portions 88 of load cells 52 and theassociated upper surfaces 92 of portions 76 of brackets 74 as also shownin FIG. 6.

As mentioned above, bodies 52 deflect in response to loads being appliedto load cells 50. When bodies deflect 52, which deflection isfacilitated by necked-down portion 90 having a smaller cross sectionalarea across the width of bodies 52 than the cross sectional area ofportions 86, 88, the gap between bottom surfaces 94 of portions 88 andsurfaces 92 of portions 76 of brackets 74 decreases. When the maximumload is applied to load cells 50, portions 88 of bodies 52 contactportions 76 of brackets 74 thereby preventing portion 88 from movingdownwardly any further even if additional load beyond the “maximum”amount is applied to load cells 50. This feature is well known in theart and prevents overflexing of portions 90 of bodies 52 to preventdamage to portion 90 or to the sensors 54, such as strain gages, of loadcells 50.

Brackets 74 are coupled to end portions 68 of respective frame members62 by fasteners, such as illustrative bolts 96, which extend throughapertures 98 in the upper regions of side portions 78 of brackets 74 andwhich are threaded into respective threaded apertures 100 provided inend portions 68 of frame members 62. Thus, end portions 68 of framemembers 62 are situated between side portions 78 of brackets 74 and loadcell bodies 52 are situated beneath end portions 68 of frame members 62in the illustrative example. In other embodiments, brackets 74 areomitted and load cells 50 mount directly to lift mechanisms 28, 30. Loadcells 50 are coupled to lift mechanisms 26, 28 so that, as liftmechanisms 26, 28 extend and retract to change the elevation of theassociated end of upper frame 26, load cells 50 move upwardly anddownwardly, respectively, without tilting.

When some load cells tilt, a cosine error typically is introduced in theoutput signals from the associated sensors which may lead toinaccuracies in the weight reading, unless the angle of tilt is sensedand appropriate cosine error compensation software is provided tocorrect the error. However, in the illustrative embodiment, no suchangle sensors and cosine error compensation software is needed becauseload cells 50 do not tilt when lift mechanisms 28, 32 are raised andlowered. In other embodiments, bed 20 may have lift mechanisms thatresult in tilting of load cells 50 when the lift mechanisms are raisedand lowered. The appropriate angle sensors and cosine error compensationsoftware may be provided in such embodiments, if desired.

Each of load cell assemblies 46, 48 further comprises a stud 110extending substantially horizontally from the associated load cell body52 as shown in FIGS. 2, 3, and 6. Each illustrative stud 110, one ofwhich is shown in FIG. 4, includes a hex nut portion 112, a threadedportion 114 on one side of portion 112, and a cylindrical portion 116 onthe other side of portion 112. Portion 114 of stud 110 is threaded intoa threaded hole 118 formed in load cell body 52 until hex nut portion112 abuts a vertical end surface of portion 88 of body 52. Cylindricalportions 116 of load cell assemblies 46, 48 extend laterally withrespect to bed 20 and therefore, are substantially perpendicular to thelong dimension of bed 20. In other embodiments, the portion of stud 110extending outwardly from body 50 has some other shape, such as sphericalor frustoconical, in lieu of being cylindrical.

Load cell assemblies 46 near the head end 30 of bed 20 each have amovable stud receiver 120, shown, for example, in FIGS. 2 and 4, andload cell assemblies 48 near the foot end 34 of bed 20 each have a fixedstud receiver 122, shown, for example, in FIG. 3. Each of stud receivers120, 122 has a space 124 that receives cylindrical portion 116 ofassociated stud 110. In the illustrative embodiment, space 124 is acylindrical bore having a diameter that is slightly larger than thediameter of cylindrical portion 116. Thus, cylindrical portion 116 isreceived in space 124 with a loose fit. In FIGS. 2 and 3, load cells 50,frame members 62, brackets 74, and studs 110 are shown pulled away fromstud receivers 120, 122 so that respective spaces 124 can be seen.

Each of studs 110 has a substantially horizontal axis 126 as shown inFIGS. 2, 3, and 6. When one or the other of lift assemblies 28, 32 isoperated to raise or lower the respective end 30, 34 of upper frame 26while the other of lift assemblies remains stationary, stud receivers120, 122 rotate relative to studs 110 about respective axes 126. Forexample, if both lift assemblies 28, 32 are raised by a substantiallyequivalent amount such that upper frame 26 is supported by liftassemblies 28, 32 in a substantially horizontal position, shown in FIG.7, lowering of lift assembly 32 while lift assembly 28 remainsstationary results in movement of upper frame 26 from the horizontalposition to a reverse Trendelenburg position, shown in FIG. 8. On theother hand, if lift assemblies 28, 32 support upper frame 26 in thehorizontal position of FIG. 7, then lowering of lift assembly 28 whilelift assembly 32 remains stationary results in movement of upper frame26 from the horizontal position to a Trendelenburg position, shown inFIG. 9.

Frame 26 comprises a pair of longitudinal frame members 128, each ofwhich comprises an elongated main member 130 and a pair of channelmembers 132 that are fastened, such as by welding, to end regions of theassociated member 130 as shown in FIGS. 1–4. Frame 26 also comprises aplurality of lateral frame members 134, portions of which are shown inFIGS. 2 and 3. Each of channel members 132 has a top wall 136, a bottomwall 138, and a side wall 140 extending between walls 136, 138 as shownin FIGS. 2–6. Thus, each channel member 132 is C-shaped in cross sectionto define a channel 142 in which the associated stud receiver 120, 122is situated.

As frame 26 tilts from the horizontal position of FIG. 7 to either thereverse Trendelenburg position of FIG. 8 or the Trendelenburg positionof FIG. 9, stud receivers 120, 122 tilt along with frame 26 and rotateabout axes 126 of studs 110 as mentioned above. Stud receivers 122 arefixed in position relative to frame 26 whereas stud receivers 120 areable to move relative to frame 26. Thus, when frame 26 is in thehorizontal position, the head end of stud receivers 120 are a firstdistance 144 away from the head end of channel members 132 as shown inFIG. 7. When frame 26 is in the reverse Trendelenburg position or in theTrendelenburg position stud receivers 120 are a second distance 146 awayfrom the head end of channel members 132 as shown in FIGS. 8 and 9.Second distance 146 is smaller than first distance 144. In theillustrative example, the angle of tilt of frame 26 relative tohorizontal is substantially the same in the reverse Trendelenburgposition as in the Trendelenburg position and therefore, distance 146 issubstantially the same regardless of whether frame 26 is in theTrendelenburg or reverse Trendelenburg position. In other embodiments,however, frame 26 may tilt more or less than the illustrative embodimentand the maximum angle of tilt in opposite directions may not besubstantially equivalent.

To reduce friction between stud receivers 120 and channel members 132 offrame 26 during relative movement between stud receivers 120 and frame26, load cell assemblies 46 each have a set of rollers 148 coupled tostud receivers 120 as shown in FIGS. 2-9. Rollers 148 each contact anundersurface 150 of the top wall 136 of each associated channel member132 and roll upon the respective undersurface 150 as frame 26 tiltsrelative to base frame 22. In other embodiments, a set of rollers arecoupled to frame 26 and contact associated moveable stud receivers. Byproviding rollers 148 between stud receivers 120 and frame 26, stickseize between stud receivers 120 and frame 26 is significantly reduced,or altogether eliminated, as are side loads on studs 110, therebyimproving the accuracy of load cell assemblies 46, 48.

Illustrative stud receivers 120 each comprise a first exterior verticalwall 152 and a second exterior vertical wall 154 that is spaced from,but substantially parallel with, wall 152 as shown in FIGS. 2, 4, and 6.Illustrative stud receivers 120 also each comprise an interior verticalwall 156 and an interior horizontal wall 158 as shown in FIGS. 4 and 5.Walls 156, 158 interconnect and span the gap between walls 152, 154.Rollers 148 are received in roller-receiving pockets 160 that aredefined in stud receivers 120 between associated walls 152, 154 oneither side of the associated wall 156 and above the associated wall158. While a majority of each roller 148 is situated inside theassociated pocket 160, a slight amount of the top portion of each roller148 extends upwardly beyond the top surface of stud receivers 120. Inthe illustrative embodiment, each of pockets 160 is open at the topsurface and at respective end surface of the associated stud receiver.Thus, in the illustrative embodiment, two pockets 160 are provided ineach stud receiver 120 to accommodate two rollers 148. In otherembodiments, more or less than two rollers 148 may be coupled to eachstud receiver 120.

Stud receivers 120 comprise a pair of cylindrical bosses 162 appended toan outer surface of wall 152 as shown in FIG. 4. A first set of holes164 extend through bosses 162 and through wall 152 and a second set ofholes 166 extend through wall 154. Each hole 166 is aligned with, but isslightly smaller in diameter than, an associated one of holes 164. A setof shafts 168 extend through pockets 160 across the gap defined betweenwalls 152, 154. Rollers 148 are each mounted on a respective one ofshafts 168 for rotation about a respective roller axis 170. Each of axes170 is substantially horizontal and substantially parallel with the axes126 of studs 110 as shown in FIG. 6. Each bore 124 is formed in theassociated stud receiver 120 through wall 152 and into an area wherewalls 156, 158 meet as shown in FIG. 5. Thus, roller axes 170 define aplane that is situated above the associated axis 126.

Shafts 168 each have a large diameter portion 172 and a small diameterportion 174 as shown in FIG. 4. Each shaft 168, therefore, has anannular shoulder 176 extending between portions 172, 174. Each portion174 is at one end of the associated shaft 168 and is sized for receiptin an associated one of holes 166 provided in the corresponding wall154. An opposite end of each shaft 168 is provided by an end region ofthe associated portion 172 and is sized for receipt in an associated oneof holes 164 provided in bosses 162 and the corresponding wall 152. Eachshoulder 176 abuts a respective wall 154. In some embodiments, bosses162 are heat staked over the ends of portions 172 of shafts 168 toretain shafts 168 in place relative to stud receivers 120. In otherembodiments, shafts 168 are retained in place in some other manner, suchas by press fitting in holes 164 and/or holes 166 or by use of retainingclips or pins that are coupled to shafts 168 and/or to stud receivers120.

To reduce friction between rollers 148 and shafts 168, a set of DUbushings 178 are interposed between each roller 148 and the respectiveshaft 168 as shown in FIGS. 4 and 5. Each bushing 178 is press fit intoa bore 180 of the corresponding roller 148. In addition, each bushing178 has a bore 182 in which portion 172 of an associated shaft 168 isreceived with a loose fit. In alternative embodiments, bushings 178 arereplaced by bearings with rolling elements, such as ball bearings,needle bearings, cylindrical roller bearings, or the like. It has beenfound that using bearings with rolling elements in load cell assemblies46 improves the accuracy of the weight reading as compared to load cellassemblies 46 using bushings 178, but bushings 178 are usually lessexpensive than bearings with rolling elements.

Stud receivers 122 each have a shape that is substantially similar tothe shape of stud receivers 120. However, stud receivers 122 do not haveany rollers 148, shafts 168, or bushings 178 coupled thereto. To fixstud receivers 122 in place relative to frame 26, a set of fasteners,such as bolts 184, shown in FIG. 4, are inserted through associatedholes 186 in walls 140 of channel members 132 and through holes 188 instud receivers 122, and then associated nuts 190, shown in FIG. 3, arethreaded onto the ends of bolts 188. Illustrative holes 188 extendthrough walls 152, 154, 158 of stud receivers 120, 122. Bolts 184 areshown in FIG. 4 to indicate that, if desired, stud receivers 120 can befixed to frame 26 at the head end thereof and stud receivers 122 at thefoot end of frame 26 can have rollers 148 coupled thereto. In otherwords, either of stud receivers 120, 122 can be fixed to frame 26 solong as the other of stud receivers 120, 122 is movable relative toframe 26. Thus, stud receivers 120, 122 serve as carriers to carry frame26, one of stud receivers 120, 122 being a fixed carrier and the otherof stud receivers 120, 122 being a rolling or movable carrier.

In the illustrative example of load cell assemblies 46, 48, load cellbodies 52, brackets 74, studs 110, rollers 148, shafts 168, bushings178, and fasteners 80, 96, 184, 190 are made of metal material and studreceivers 120, 122 are made of a plastic material. For example, in oneembodiment, load cell bodies 52 are aluminum, studs 110 are steel, suchas 4140 C.D.S. steel or 4142 C.D.S. steel, rollers 148 are steel, andstud receivers 120, 122 are M90 Acetal material. In other embodiments,stud receivers 120, 122 may have main bodies made of a metal material,or any other material having suitable load-carrying capability, and mayhave plastic liners that are received in cavities provided in the mainbodies and that have bores 124 provided in the liners to receiveassociated studs 110. In still further embodiments, stud receivers 120,122 may be made of metal and studs 110 may have a coating ofantifriction material which serves as a liner between the studs and theassociated stud receivers.

In an alternative embodiment, stud receivers 120, 122 each have atriangular hole or bore 192 as shown in FIGS. 10 and 11. Each hole 192is defined, in part, by a pair of inclined surfaces 194. Part ofcylindrical portions 116 of studs 110 are received in bores 192 andcontact the associated pair of inclined surfaces 194. Thus, in theembodiment of FIGS. 10 and 11, cylindrical portions 116 of studs 110engage stud receivers 120, 122 along two lines of contact. As comparedto the embodiment of FIGS. 1–9, in which studs 110 engage stud receivers120, 122 along one line of contact, the stress levels betweencylindrical portions 116 of studs 110 and any one of inclined surfaces194 are less than the stress levels between cylindrical portions 116 ofstuds 110 and the cylindrical surface that defines bores 124 in studreceivers 120, 122. In the illustrative example, apexes or corners 196of each triangular hole 192 are rounded and are spaced from theassociated stud 110. In still other embodiments, inclined surfaces 194may be provided as part of holes or bores that are square,diamond-shaped, hexagonal, octagonal, and so on. While illustrativesurfaces 194 are substantially flat, in some embodiments, surfaces 194may be either concave or convex, as desired, yet still provide two linesof contact with cylindrical portions 116 of studs 110. In alternativeembodiments, studs 110 may have spherical portions providing two pointsof contact with surfaces 194.

Those skilled in the art will appreciate that, although load cellassemblies 46, 48 are described herein as being coupled to frame 26 andto frame members 62 of lift mechanisms 28, 32, it is within the scope ofthis disclosure for load cell assemblies 46, 48 to couple to any type ofstructure or support. Therefore, the term “structure” as used in theclaims is intended to be non-limiting and to mean any and all types ofstructures such as frames, bases, supports, members, pedestals, decks,surfaces, plates, panels, beams, and so forth.

Although certain illustrative embodiments have been described in detailabove, variations and modifications exist within the scope and spirit ofthis disclosure as described and as defined in the following claims.

1. A combination comprising a first structure, a second structure, aload cell coupled to the first structure, the load cell comprising aload cell body and a sensor, the sensor providing an output signalindicative of an amount of load applied to the load cell, a studextending away from the load cell body, a stud receiver having a spacein which a portion of the stud is received, and a set of rollers coupledto one of the stud receiver and the second structure and contacting theother of the stud receiver and the second structure.
 2. The combinationof claim 1, wherein the space comprises a substantially cylindrical borein which the portion of the stud is received.
 3. The combination ofclaim 2, wherein at least part of the portion of the stud received inthe substantially cylindrical bore is substantially cylindrical and hasa stud diameter smaller than a bore diameter of the substantiallycylindrical bore.
 4. The combination of claim 1, wherein the spacecomprises a substantially triangular bore in which the portion of thestud is received.
 5. The combination of claim 4, wherein at least partof the portion of the stud received in the substantially triangular boreis substantially cylindrical.
 6. The combination of claim 5, wherein thesubstantially triangular bore is defined, in part, by two inclinedsurfaces that engage different portions of the stud along a pair ofcontact lines.
 7. The combination of claim 4, wherein the substantiallytriangular bore has three apexes that are spaced from the stud.
 8. Thecombination of claim 1, wherein the stud receiver rotates about the studwhen the second structure tilts relative to the first structure.
 9. Thecombination of claim 1, wherein the set of rollers roll upon the secondstructure when the second structure tilts relative to the firststructure.
 10. The combination of claim 1, wherein the stud extendssubstantially horizontally relative to the load cell body along a firstsubstantially horizontal axis and each roller of the set of rollers isrotatable about a respective second substantially horizontal axis. 11.The combination of claim 10, wherein the set of rollers comprises atleast two rollers and the second substantially horizontal axes of the atleast two rollers define a plane situated above the first substantiallyhorizontal axis.
 12. The combination of claim 1, wherein the studreceiver comprises a pair of roller-receiving pockets, the set ofrollers comprises a pair of rollers, and at least a portion of eachroller of the pair of rollers is received in a respective pocket of thepair of roller-receiving pockets.
 13. The combination of claim 12,wherein the stud receiver comprises a horizontal wall underlying thepair of roller-receiving pockets and a vertical wall situated betweenthe pair of roller-receiving pockets.
 14. The combination of claim 12,wherein the roller-receiving pockets are each open at a top surface andat respective end surfaces of the stud receiver.
 15. The combination ofclaim 1, wherein the stud receiver has a top surface and a part of eachroller of the set of rollers extends upwardly beyond the top surface ofthe stud receiver.
 16. The combination of claim 1, wherein the studreceiver has a pair of vertical walls and at least part of each rollerof the set of rollers are situated between the pair of vertical walls.17. The combination of claim 16, further comprising a set of shaftsextending across a gap defined between the pair of vertical walls andeach roller of the set of rollers is mounted for rotation on arespective shaft of the set of shafts.
 18. The combination of claim 17,further comprising a set of bushings, each bushing being interposedbetween a respective roller of the set of rollers and the associatedshaft.
 19. The combination of claim 17, further comprising a set ofbearings with rolling elements, each bearing being interposed between arespective roller of the set of rollers and the associated shaft. 20.The combination of claim 17, wherein a first vertical wall of the pairof vertical walls has a first set of holes, a second vertical wall ofthe pair of vertical walls has a second set of holes, each shaft has afirst end received in a respective hole of the first set of holes, andeach shaft has a second end received in a respective hole of the secondset of holes.
 21. The combination of claim 20, wherein each of the firstholes has a first diameter that is larger than a second diameter of eachof the second holes and each shaft of the set of shafts has a shoulderthat contacts the second vertical wall.
 22. The combination of claim 20,wherein the stud receiver has a set of shaft retainers coupled to afirst vertical wall of the pair of vertical walls and each shaftretainer is heat staked over an end of a respective shaft.
 23. Thecombination of claim 1, further comprising a bracket that couples theload cell body to the first structure.
 24. The combination of claim 23,wherein the bracket has a bottom portion that underlies the load cellbody and at least one side portion that extends between the bottomportion and the first structure, the at least one side portion beingfastened to the first structure, and the load cell body being fastenedto the bottom portion.
 25. The combination of claim 23, wherein thebracket comprises a bottom portion and two side portions extendingupwardly from the bottom portion such that the bracket is U-shaped incross section, the load cell body sits atop the bottom portion, and atleast part of the first structure is situated above the load cell bodyand between the two side portions of the bracket.
 26. The combination ofclaim 1, wherein the stud receiver is made of a plastic material and thestud is made of a metal material.
 27. The combination of claim 1,wherein the first structure comprises a lift mechanism of a patientsupport apparatus and the second structure comprises a frame of thepatient support apparatus.
 28. The combination of claim 27, wherein thepatient support apparatus has a length dimension defined between a headend and a foot end of the patient support apparatus and the stud has anaxis that is substantially perpendicular to the length dimension of thepatient support apparatus.
 29. The combination of claim 27, wherein thelift mechanism is extendable and retractable to change an elevation ofthe frame and the load cell body is coupled to the lift mechanism so asto move upwardly and downwardly without tilting as the lift mechanismextends and retracts.
 30. The combination of claim 27, wherein the liftmechanism comprises a telescoping column and a first frame membercoupled to an upper region of the telescoping column, an end portion ofthe first frame member extends from the telescoping column toward asecond frame member of the upper frame, and the load cell body iscoupled to the end portion of the first frame member.
 31. Thecombination of claim 27, wherein the upper frame comprises a framemember having a C-shaped cross section defining a channel in which thestud receiver is situated.
 32. The combination of claim 31, wherein theframe member comprises a top wall, a bottom wall, and a side wallextending between the top and bottom walls and wherein the set ofrollers contact an undersurface of the top wall.
 33. The combination ofclaim 27, wherein the lift mechanism is operable to change the elevationof the frame and, as the frame changes elevation, the set of rollersroll on the frame.
 34. The combination of claim 1, wherein the space ofthe stud receiver is defined, in part, by a pair of inclined surfaces,at least a portion of the stud is received in the hole and contacts thepair of inclined surfaces.
 35. The combination of claim 34, wherein thespace of the stud receiver comprises a triangular hole that is bounded,in part, by the pair of inclined surfaces.
 36. The combination of claim35, wherein corners of the triangular hole are rounded.
 37. Thecombination of claim 1, wherein the sensor comprises at least one offollowing: a strain gage, a resistive element, a capacitor, a transducerusing shaped magnetic field technology, an optical sensor, a transducerthat emits electromagnetic energy, a transducer that receiveselectromagnetic energy, or a linear variable displacement transducer.38. The combination of claim 1, wherein the stud has a cylindricalportion.
 39. The combination of claim 1, wherein the stud has aspherical portion.
 40. The combination of claim 1, wherein the load cellbody has a threaded hole and the stud has a threaded portion thatthreads into the threaded hole.